Pyridine and pyridine derivatives are effectively used as solvents and also as catalysts. They are used in the synthesis of many different products which are used as medicines, vitamins, food flavorings, paints, dyes, rubber products, adhesives, insecticides and herbicides.
The most general industrial synthetic reaction for the manufacture of pyridine bases is by the catalytic condensation of aldehydes and/or ketones with ammonia. The reaction is usually carried out at 350-500° C. and at atmospheric pressure in the presence of alumino-silicate catalyst. Acetaldehyde, formaldehyde (in the form of formalin), and ammonia are fed to a catalyst-containing reactor, where pyridine and alkyl pyridines are formed as the major product. A wide variety of catalysts, reactants, and reaction conditions are reported in known art. “Pyridine and Pyridine Derivatives”, Goe, Gerald L., Kirk-Othmer, 3rd Edition, Vol. 19, John Wiley & Sons, p. 454 (1978); “Synthetic and Natural sources of the Pyridine Ring”, Bailey et al., pp. 1-252 in “Heterocyclic Compounds”, Volume 14, “Pyridine and Its Derivatives”, John Wiley & Sons, New York (1984), all of which are incorporated by reference in their entirety herein.
Pyridine and pyridine derivatives present in the aqueous mass are extracted by suitable method. A wide variety of methods have been applied to the problem of the separation of pyridine and pyridine derivatives. The pyridine-water azeotrope has been separated in accordance with conventional techniques e.g., by conventionally breaking the water-pyridine azeotrope by the addition of suitable solvent followed by fractional distillation to prepare substantially dry pyridine. The solvent is recovered from pyridines by distillation and recycled back to the recovery column.
Several processes are disclosed in prior patent disclosures for the separation of pyridine or pyridine derivatives from aqueous solutions by using different solvents.
Benzene is most commonly used for the recovery of pyridine and picolines from the aqueous reaction mass. See ref. “Pyridine and Pyridine Derivatives” Shimizu et al p. 399 in “Ullman's Encyclopedia of Industrial Chemistry”, Vol. A22, 5th Ed.; Elvers, B., Hawkins, S., Russey, W., Schulz, G., Eds., VCH Publishers, Weinheim (1993).
U.S. Pat. No. 4,883,881, discloses the process in which pyridine was separated from pyridine-water azeotrope by adding benzene thereto and distilling the resultant mixture to recover substantially anhydrous pyridine.
However, benzene loss during the process results in the concern like the cost of environmental protection measures, occupational safety, increased fire risks and additional investments in hazardous waste disposal costs. Besides, the use of benzene has been banned throughout a number of industries because of its hazardous nature. Therefore, there is an urgent need to address these issues, especially when the process is implemented at commercial scale.
U.S. Pat. No. 2,058,435 reported a process in which aqueous solutions of pyridine and its homologues are subjected to extraction with highly efficient extracting agents, which are non-solvents with respect to water. The process comprises the recovery of pyridine from its aqueous solution with any one of a number of solvents such as benzene, trichloroethylene, isopropyl ether, pseudo-cumene, cyclohexane, hexane and the like.
European Patent No. EP1,346,757 discloses liquid-liquid extraction with a solvent consisting of a fluorinated fluid selected from either hydrofluoropolyethers, hydrofluoroethers, hydrofluorocarbons and/or their mixtures with perfluoropolyethers and/or perfluorocarbons.
U.S. Pat. No. 5,100,514 describes a method for separating pyridine from water using certain organic compounds, as the agent in azeotropic or extractive distillation. Typical examples of effective agents are: by azeotropic distillation, methyl isoamyl ketone and propylene glycol dimethyl ether; by extractive distillation, isophorone and sulfolane.
Other conventional techniques can also be used, e.g., drying operations, extraction, saltation, redistillation, etc., in accordance with fully conventional considerations, e.g., as discussed in any of a wide variety of relevant texts, e.g., see ref. “Chemist's Companion”, Gordon, Arnold J. et al., John Wiley and Sons (1972).
Park, Choon Ho. et al in Journal of Applied Polymer Science (1999), 74(1), 83-89, has discussed the pervaporation separation through a poly(acrylonitrile-co-vinylphosphonic acid) membrane. Polyacrylonitrile (PAN)-based copolymers containing phosphonic acid moiety were synthesized for dehydration of aqueous pyridine solution. The in situ complex, formed between the vinylphosphonic acid (VP) moiety in the membrane and the pyridine in the feed, enhanced separation capacity of poly(acrylonitrile-co-vinylphosphonic acid) (PANVP) membranes. All the PAN-based membranes containing phosphonic acid were very selective toward water. The pervaporation performances of PANVP membranes depended on the content of the phosphonic acid moiety in the membrane and operating temperature. The pervaporation separation of water/pyridine mixtures using PANVP membranes exhibited over 99.8% water concentration in permeate and flux of 4-120 gm−2h−1 depending on the content of vinylphosphonic acid and operating temperature.
U.S. Pat. No. 6,087,507 describes a method of continuously separating pyridine or pyridine derivatives from aqueous solutions by extraction, wherein supercritical fluid is employed to extract the pyridine material from liquid media. The method of the invention, in particular, extracts pyridine or pyridine derivatives from aqueous solutions with pressurized carbon dioxide, which is used under pressure, or in the liquid state, or in the near critical state or in the supercritical state. The operating system is a continuously operating extraction system, so that a part, or all, of the pyridine and/or pyridine derivatives are transferred from the aqueous phase to the carbon dioxide phase, and thereafter the aqueous phase and carbon dioxide phase are separated from each other; and the pyridine and/or pyridine derivatives are separated from carbon dioxide; and the extract containing pyridine and/or pyridine derivatives is thereby obtained. Preferred temperatures for the pyridine and/or pyridine derivative contacting with carbon dioxide are from 5 to 80° C.; and preferred pressures range from 60 to 300 bar. However, the process is not suitable at, industrial scale because extraction was done at very high pressure (60 to 300 bar). This makes extraction process operationally unfriendly and highly capital intensive at industrial scale.
The processes disclosed in the prior art used hazardous and industrially unsuitable solvents. Some of the solvents disclosed are highly unsafe to handle in commercial scale manufacturing processes. Moreover most of the processes discussed in prior art are for the separation of pyridine or pyridine derivatives from aqueous solutions only, not from the complex manufacturing reaction mass. The problems associated with the above prior art can be overcome by using commercially viable; operational and eco-friendly process and solvent to avoid all the above-mentioned problems in the known prior art.